I am rapidly coming to the conclusion that if you must fit a heat pump then air source might be the best longer term option.

There are already lots of threads on GSHP Sagecaster so don't forget to read them too.

24kW sounds awfully large for a UK climate - we have a 14kW pump in a 425sqm house in cold Quebec - a climate far harsher than anywhere in Scotland. EIther the 2007 building regs are rubbish, or something is seriously wrong with your levels of insulation and airtightness. Or does this 24kW also include domestic hot water?

As for cost savings - what are you comparing with? Natural gas, oil, haggis guano? Don't forget that current energy costs are different from future energy costs. Of course, your guess is as good as mine as to which will rise faster, but they will all rise.

Paul in Montreal.

Posted By: Paul in Montreal24kW sounds awfully large for a UK climate - we have a 14kW pump in a 425sqm house in cold Quebec - a climate far harsher than anywhere in Scotland. EIther the 2007 building regs are rubbish, or something is seriously wrong with your levels of insulation and airtightness. Or does this 24kW also include domestic hot water?

Paul in Montreal.

Yes it does include the hotwater.

Regarding 2007 building regs, they are appear to be very good for insulation, as I have seen a calculation where doubling the insulating layer equates to less than a 4% reduction in energy consumption. Money is better spent in using a larger Ground Area.
This is the company involved and they have a good reputation--
http://www.invisibleheating.co.uk/ground-source-heat-pumps-g.asp" >Invisible Heating

Those "invisble heating" people are full of it:

"All IHS heat pumps yield a COP from 4 up to to 9 depending on the installation method used."

Never seen anyone anywhere claim a COP of 9.

Paul in Montreal.

Posted By: Paul in Montreal
Never seen anyone anywhere claim a COP of 9.

Paul in Montreal.

Agreed, its very misleading

Seems to be a theme of air tightness here, is there a means of assessing this? Frustratingly, uk building regs insist on a vent in a room where an open fire is used, this must compromise air tightness? Is there a means around this?

Sagecaster, Cant say if it's cost effective or if it delivers yet but Im also in rural Scotland (far NW) and have also been looking at alternative heat pump options including those from the company you mention. We will also have radiators, have discounted the idea of an air source heat pump due to being on the coast (salt air) and plan to have a wood burner as a backup in times of power cuts but this will be for space heating only.

Al I can say is if you're fixed on a heat pump have a look at two or three alternatives and speak to the vendors to get a feel for how their proposed system will work and how well it will fulfill your requirements. I have found that theres a huge variations in sizing, hot water delivery, ground collectors and more importantly, their willingness to engage with the customer. Dont think they realise what a big investment this is for many people. Also, few companies (including the one you mentioned) are prepared to provide an installation service preferring to sell the hardware, leave installation to the customer and then return to commission the system (at a cost.)

Hope that helps.

That is a good point Tuna (I've just noticed the area...). Maybe in a large house, the heat generated by the occupants and appliances, lighting etc will never be sufficient to make a central heating system redundant? Perhaps it is better to build a smaller house and have separate out buildings for occasional uses, like a guest bedroom with ensuite, which are heated only when required?

Design of building, manner of occupation and source of heat interact, and the whole subject is vastly more complex than popularly imagined, even by the gurus on this web site..........

In my opinion, Funcrusher's post says it all, couldn't put it better. Oh, and a 15kW heat pump would be more accurately sized for a property of 340 m2 built to current regs.

Posted By: DantenzDesign of building, manner of occupation and source of heat interact, and the whole subject is vastly more complex than popularly imagined, even by the gurus on this web site..........

That's why trained professionals should be used to design and install such systems, especially as buildings become more energy efficient. Gone are the days where any old joe plumber could just shove in a large gas fired boiler + rads and have a working system.

Posted By: (GBP) Keitht looks like GSHP, unless very carefully designed could easily to suffer from falling COP over the years as the temp of the ground gets depleted. Also I've just been told that many GSHP units include a resistance heater for backup. Nasty?

Not if the ground loop is properly designed - which, if a trained professional is used ... well, you get the drift. Nothing wrong with resistance auxiliary heating either. This allows the unit to be sized more appropriately than worst-case conditions. This results in a smaller (and hence cheaper) unit and loop field with lower running costs. The resistance heat just kicks in on those rare occasions when it's needed. Over here in a bipolar climate (cold/dry in winter hot/humid in summer) a GSHP does both A/C and heating and is usually sized for about 80% of the worst case heating load. This actually covers about 98% of a typical winter's operating time and prevents and oversized unit giving poor A/C performance in the summer when humidity removal (i.e. latent heat) is key to comfort, not absolute air temperature.

Posted By: sagecasterI am an engineer by profession, so have good handle on the principles and thermodynamics and am not sold on the principle of AS.

Not sure I understand what you mean there sagecaster. The same principles of operation are used by both air and ground source heat pumps. In fact, ASHPs may be more efficient than GSHPs in the "shoulder" season. In a climate that doesn't go below freezing, an ASHP is probably a better bet than a GSHP, except for the UK's typical aversion to forced-air delivery which is common in most of the rest of the world and would lead to lower prices due to economies of scale. That said, there are many Asian "mini-split" systems which have incredible COPs that would be perfect for the UK climate.

Paul in Montreal

http://www.nottenergy.com/energy-costs-comparison2

..claims ASHP costs 1.75 times as much to run than GSHP, presumably all due due to worse COP since cost of electricity is same.

Time will tell on the falling COP theory. Results of early installations due in soon and I think they will point the way I predict.

Don't get me wrong In no way am I suggesting that anyone installs ASHP.

Resistance heating will have a COP of what, minus 5 to 1 Paul?

Posted By: sagecasterAir is a very poor conductor of heat and we avoided using it as a means of heat transfer in thermo dynamic design. Sometimes using air was unavoidable as the simplest design solution dictated that we use air, but it was never efficient.

I think you're confusing efficiency with effectiveness. The distribution medium has no "efficiency", only the source of energy production has an associated efficiency. As much as air is a poor conductor, it's the thermal capacity that's important. The majority of homes in North America are heated and cooled with forced air distribution systems (with various sources of heat, ASHP and GSHP amongst them). The trick with air is to move sufficient volume to provide the heat/cool delivery required comfortably. The outside unit of an ASHP may have huge volumes of air pass over it - it's efficiency is determined by the design of the coils used together with the refrigerant and compressor system as well as the approach used for defrosting the coils where necessary. The poor conduction of air has no real bearing on the efficiency of an ASHP - it's the temperature of the air that counts and the mass flow rate. At a given air temperature, an ASHP is as efficient as a GSHP operating at the same inlet water temperture (assuming no defrost is required). The main advantage of GSHP is that the source temperature is relatively constant in winter when the demand is highest; an ASHP has a falling capacity as the demand on it increases, making it much less effective in winter than a GSHP of the same capacity.

Paul in Montreal.

Posted By: (GBP) KeithWhat can I say Paul. I think one of us is being a bit thick or obstinate on this subject! I'm happy to hold my hand up to both charges but what about you? Please remind us all of your interest here. Are you on someone's payroll?

I'm not sure what you mean thick or obstinate. I'm just pointing out that the source of heat is where efficiency is measured, not the distribution system. Resistance backup is not a bad thing if designed in properly as I pointed out. I have no commercial interest whatsover and I'm definitely not on anyone's payroll in that field. I'm just a happy user of two GSHP systems - one in an old house and one in a new. There's a lot of mis-information and mis-understanding out there and I just try to counterbalance that. People are also getting way overcharged - they systems are pretty simple and should not be particularly expensive.

Paul in Montreal.

The price for the retrofit of our old house (185m2 + 83m2 heated basement so about the same size) using a 12.3kW water-to-air GSHP broke down like this:

Heatpump plus ductwork and installation and commissioning: Can$16810
420 foot vertical borehole and pipework and connection: Can$5880 (quote as Can$14 per foot)

Total is about £10k more or less. There was quite a lot of labour involved in installing all the ductwork throughout the house. The system also includes a desuperheater to preheat the domestic hot water supply. Our hot water is a gas-fired 225l tank and our monthly gas consumption in the coldest months goes down to less than 10m3 a month (or around Can$1.80 ish).

BTW commissioning includes setting the flow rate properly and measuring the entering/leaving water temperatures to ensure correct performance (otherwise you'd have no idea of the actual COP).

We got grants of around Can$4800 - not specifically for the heatpump but just for the improvement in energy efficiency of the pre- versus post-renovation house.

A friend of mine is a certified energy auditor and installed his own system. He used a 12.3kW water-to-water GSHP manufactured by Trane - the cost to him was Can$1500 for the heatpump. Water-to-water pumps are cheaper than water-to-air because there's no air handler. My understanding is that most systems in the UK are effectively water-to-water rather than water-to-air with no reversibility (to provide A/C). All systems over here are reversible and provide A/C in the summer.

Paul in Montreal.

Posted By: jamesingramI heard canada still high up on the world pollutors league though , which surprised me a bit

It's not so surprising when you consider that

(o) Canada is the second largest country on earth
(o) Canada has the coldest capital city on earth
(o) Population density is low
(o) Distance between cities is large
(o) Food doesn't grow well when there's snow on the ground for months on end
(o) A cold climate needs a lot of heat to make it livable in winter
(o) Land is cheap and hence houses tend to be much larger than the UK

I think Canada has the highest per-capita energy use of any country. What surprises me is that, if I recall correctly, Australia is #3.

Paul in Montreal